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From: "vries at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>
To: gdb-prs@sourceware.org
Subject: [Bug gdb/23710] gdb is slow and memory hungry consuming debug
 generated with LTO by GCC
Date: Fri, 20 Mar 2020 09:06:06 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D23710

--- Comment #14 from Tom de Vries <vries at gcc dot gnu.org> ---
(In reply to Tom de Vries from comment #5)
> (In reply to Richard Biener from comment #0)
> > gdb takes ~10s to process a LTO bootstrapped cc1 binary and another two
> > seconds
> > when setting the first breakpoint.  It also has allocated 1.6GB memory =
at
> > that point (compared to ~200MB for a non-LTO binary).
>=20
> There's a setting "maint set/show dwarf max-cache-age" which defaults to =
5.
>=20
> Using a higher setting, I get the following reduction in real execution t=
ime:
> - 10    :  1.5%
> - 100   : 12.5%
> - 316   : 16.5%
> - 1000  : 16.5%
> - 10000 : 16.5%
> - 100000: 15.5%
>=20
> Note: adding the setting to the gdb command line using -iex to make sure =
it
> gets set _before_ loading the exec):
> ...
> $ gdb -q -nw -nx -batch -iex "maint set dwarf max-cache-age $n" -ex "b
> do_rpo_vn" cc1
> ...
>=20
> Conversely, disabling the cache by setting the value to 0 causes a real
> execution time increase of 46%.

Filed PR25703 - "set dwarf max-cache-age default of 5 is slow for
inter-CU-reference binaries".

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